This is not really an exploit but it saves lifes!
Buy a Thottbot World of Warcraft: Dreamless Sleep Potion (its cheap) in the Auction House or somewhere.
If you falling down from anywhere and you think you will die then drink it short before you are landing and you will sleep for some seconds.
When you are waking up again you will fall to ground but you will not take falldamage because the game thinks you start falling down when you used that Potion.
Note: This is only working if you have not 100% health. If you falling down and you got 100% health the potion cannot be used.
If you have enough money you can save your life everytime - that means you can save your life when you have 100% health too. But its not cheap.
When you think you have enough money, then buy a Thottbot World of Warcraft: Flask of Petrification - It have the same effect like the other potion (its longer, 1 Minute).
The Flask of Petrification will work everytime and rescue your life when you are falling down somewhere but it costs very much gold and its better you use it to make some Alliance/Horde angry!